The cost of repairing the Dáil and the Seanad due to serious fire safety and building collapse fears is set to top €17m - more than twice as much as the €8m figure originally predicted.
Despite the surging costs, secretary general of Oireachtas services Peter Finnegan said the price tag represents "outstanding" value for the taxpayer.
Since early 2018, significant repair works have been taking place in the Houses of the Oireachtas in order to address long-standing problems in the 200-plus-year-old buildings.
The work has led to the temporary closure of the historic part of the Leinster House building and has seen the Seanad move temporarily into the nearby national museum of Ireland which is on an adjoining Kildare Street site.
The cost of the refurbishment - which is expected to conclude on August 2 before the re-opening of the facilities in early autumn - was initially predicted to be just €8m.
However, asked about revelations in Monday's Irish Examiner the true price tag is now likely to exceed €17m, Mr Finnegan told the public accounts committee meeting this is expected to be the case.
"It's not far off that," Mr Finnegan told Sinn Féin TD David Cullinane when asked about the runaway costs.
The estimated cost of the overspend is probably in the order of 15%. The reason there's an overspend is because there was a certain amount of this work that could not be known in advance.
"They were certain things stripped away, brick work, buildings, fire work, addressing some of the voids," he said.
Mr Finnegan rejected suggestions from Mr Cullinane the initial estimate was badly off target, saying "it's impossible to catch everything" and that "historic buildings" will always cost more to repair than first suggested.
The senior Oireachtas official said it was "unfortunate" that a colleague defended the costs to reporters in recent weeks by referencing the Sistine Chapel in Rome and saying "as Michelangelo said to the pope, it will cost what it will cost".
However, asked by Fianna Fáil TD Shane Cassells about what the public will think of the doubling of expected costs and the ballooning of the final price tag to more than €17m, Mr Finnegan added: "To spend €17m, and if you average that out over 200 years, it's outstanding value for money. I think the work is to an extremely high standard, and ultimately it's the people's parliament."
Meanwhile, Mr Finnegan and other Oireachtas officials were left red-faced by PAC members over related problems with the campus, highlighted by news of at least one rat in the Dáil bar this week.
In a series of remarks about the rodent visitor, Catherine Connolly told Mr Finnegan. "I take comfort from the fact they haven't deserted yet, so this ship isn't sinking yet", adding that it means it is unlikely to be an election for now.
Fine Gael TD Alan Farrell similarly asked if there is any proof the rat had anything to do with ratatouille being put on the Dáil canteen menu this week, while other PAC members also raised health and safety concerns.
Mr Finnegan, however, avoided this line of questioning, and instead said the Leinster House repair works are likely to lead to an upsurge in tourists coming to the site from early autumn, saying the expense will be seen as money well spent at that stage.